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sx05_TE_(nc6-6B).fm Page 204 Monday, June 6, 2005 11:10 AM Section 4 4 Volcanoes and Plate Tectonics Volcanoes and Plate Tectonics Objectives After completing the lesson, students will be able to F.6.1.1 Identify where Earth’s volcanic regions are located and explain why they are found in these areas F.6.1.2 Explain how hot spot volcanoes form Target Reading Skill Asking Questions Explain that changing a head into a question helps students anticipate the ideas, facts, and events that they are about to read. Answer Possible questions: Where are volcanoes found? What are hot spots? Possible answers: Most volcanoes are found along plate boundaries. A hot spot is an area where material from deep within the mantle rises and then melts, forming magma. Teaching Resources Reading Preview Key Concepts • Where are most of Earth’s volcanoes found? • How do hot spot volcanoes form? Key Terms • volcano • magma • lava • Ring of Fire • island arc • hot spot Target Reading Skill Asking Questions Before you read, preview the red headings. In a graphic organizer like the one below, ask a where, what, or how question for each heading. As you read, write the answers to your questions. Volcanoes and Plate Tectonics Question Answer Where are volcanoes found? Most volcanoes are found along plate boundaries. • Transparency F24 Preteach Build Background Knowledge Where Are Volcanoes Found on Earth’s Surface? 1. Look at the map of Earth’s Active Volcanoes on page 83. What symbols are used to represent volcanoes? What other symbols are shown on the map? 2. Do the locations of the volcanoes form a pattern? Do the volcanoes seem related to any other features on Earth’s surface? Think About It Developing Hypotheses Develop a hypothesis to explain where Earth’s volcanoes are located. In 2002, Mount Etna erupted in glowing fountains and rivers of molten rock. Located on the island of Sicily in the Mediterranean Sea, Mount Etna is Europe’s largest volcano. Over the last 2,500 years, it has erupted often. The ancient Greeks believed that Mount Etna was one home of Hephaestus, the Greek god of fire. Beneath the volcano was the forge where Hephaestus made beautiful metal objects for the other Greek gods. The eruption of a volcano is among the most awe-inspiring events on Earth. A volcano is a weak spot in the crust where molten material, or magma, comes to the surface. Magma is a molten mixture of rock-forming substances, gases, and water from the mantle. When magma reaches the surface, it is called lava. After lava has cooled, it forms solid rock. Lava released during volcanic activity builds up Earth’s surface. L1 Volcanic Eruptions Ask students: Have you ever seen a volcano? Were you on the scene, or did you see it on TV or in film? Was it erupting? What was happening? What effects did you see? How were people affected? (Answers will vary, depending on students’ experience. Encourage students to share their observations and describe details.) FIGURE 17 Lava Flow on Mount Etna A lava flow from Mount Etna in Sicily almost buried this small building. 204 ◆ For: More on volcanoes PHSchool.com Visit: PHSchool.com Web Code: cfd-1031 Students can review volcanoes in an online interactivity. 204 Skills Focus developing hypotheses L2 Time 10 minutes Tips Direct students’ attention to the map’s key to answer the questions in Step 1. Expected Outcome 1. Triangles symbolize active volcanoes; solid lines symbolize plate boundaries. 2. Yes, there is a pattern: volcanoes seem to be related to plate boundaries. Think It Over Volcanoes are concentrated along plate boundaries. Exceptions: A few volcanoes occur within plates. sx05_TE_(nc6-6B).fm Page 205 Monday, June 6, 2005 11:10 AM Instruct Earth’s Active Volcanoes Volcanoes and Plate Boundaries Asia Europe North America Asia Atlantic Ocean Africa Pacific Ocean Indian Ocean Teach Key Concepts Indian Ocean South America Australia Atlantic Ocean Key Active volcano Plate boundary Antarctica Volcanoes and Plate Boundaries There are about 600 active volcanoes on land. Many more lie beneath the sea, where it is difficult for scientists to observe and map them. Figure 18 shows the location of some of Earth’s major volcanoes. Notice how volcanoes occur in belts that extend across continents and oceans. One major volcanic belt is the Ring of Fire, formed by the many volcanoes that rim the Pacific Ocean. Volcanic belts form along the boundaries of Earth’s plates. At plate boundaries, huge pieces of the crust diverge (pull apart) or converge (push together). As a result, the crust often fractures, allowing magma to reach the surface. Most volcanoes form along diverging plate boundaries such as midocean ridges and along converging plate boundaries where subduction takes place. For example, Mount Etna formed near the boundary of the Eurasian and African plates. Diverging Boundaries Volcanoes form along the midocean ridges, which mark diverging plate boundaries. Recall that ridges are long, underwater mountain ranges that sometimes have a rift valley down their center. Along the rift valley, lava pours out of cracks in the ocean floor, gradually building new mountains. Volcanoes also form along diverging plate boundaries on land. For example, there are several large volcanoes along the Great Rift Valley in East Africa. FIGURE 18 Many of Earth’s volcanoes are located along the boundaries of tectonic plates. The Ring of Fire is a belt of volcanoes that circles the Pacific Ocean. Observing What other regions have a large number of volcanoes? Plate Tectonic Setting of Volcanoes Focus Review the types of plate boundaries, and make sketches on the board. Teach Ask: Where should volcanoes and magma chambers be included? (Fill in sketches: Volcanoes and magma chambers should occur at diverging boundaries and at two types of converging boundaries: oceanocean and ocean-continent. They are less likely to occur at transform or continent-continent converging boundaries.) Apply Ask: Why don’t volcanoes occur along the San Andreas Fault in California? (It is a transform boundary.) Would you expect volcanoes to occur along the MidAtlantic Ridge? (Yes, this is a diverging boundary.) learning modality: visual Independent Practice L2 Teaching Resources • Guided Reading and Study Worksheet: Volcanoes and Plate Boundaries Student Edition on Audio CD Use Visuals: Figure 2 For: More on volcanoes Visit: PHSchool.com Web Code: cfd-1031 Chapter 6 ◆ 205 Differentiated Instruction L1 English Learners/Beginning Vocabulary: Science Glossary Pronounce and define aloud key terms for students. Suggest that they start a personal glossary, with each term and its definition in English on one side of an index card and in the student’s primary language on the other side. They also might draw and label diagrams. learning modality: verbal L2 L2 English Learners/Intermediate Vocabulary: Science Glossary Students can expand on the activity described in Beginning by adding other scientific terms in this section: diverge, converge, subduction. Have students write sentences that use each of these words. Give students an opportunity to practice pronunciation by calling on individuals to read their sentences aloud. learning modality: verbal L2 Volcanic Regions Focus Remind students that the volcanoes in the Ring of Fire occur at converging boundaries. Teach Ask: What other volcanic belts do you see on the map? (Possible answers: in southern Europe, within Africa at the Great Rift Valley, between Africa and Arabia, in the eastern Caribbean) Apply Ask students why volcanism might occur in the Mediterranean Sea. (Possible answer: A plate boundary runs through it.) learning modality: visual Teaching Resources • Transparencies F25 and F26 Monitor Progress L2 Oral Presentation Call on students to explain what causes the Ring of Fire. Answers Figure 2 The Mediterranean area, East Africa, and the Middle East 205 sx05_TE_(nc6-6B).fm Page 206 Monday, June 6, 2005 11:10 AM Interpreting Maps L2 Materials large world map Time 10 minutes Focus Refer students to the text paragraphs that list some island arcs and continentmargin volcanic regions. Teach Ask students to locate each of the six island arcs mentioned: Japan, New Zealand, Indonesia, the Caribbean islands, the Philippines, and the Aleutians. Also ask them to locate the two regions of subductionrelated volcanism on continent margins: Andes Mountains, and the Pacific Northwest. Apply Ask students to compare these regions with the plate boundaries shown in Figure 2. learning modality: visual Hot Spot Volcanoes Teach Key Concepts FIGURE 19 Volcanoes at Converging Boundaries Volcanoes often form where two oceanic plates collide or where an oceanic plate collides with a continental plate. In both situations, an oceanic plate sinks beneath a trench. Rock above the plate melts to form magma, which then erupts to the surface as lava. How did the volcanoes in the Andes Mountains form? Mid-ocean ridge L2 Trench Isl an Trench d ar c Hot Spots Focus Ask: How would you describe the volcanoes on Hawaii? (Broad, tall volcanoes; lava fountains and flows; lava might reach ocean and cool) Teach Ask: What would happen if volcanic eruptions continued to occur on the sea floor? (Islands would form.) Is the island of Hawaii getting larger today? (Yes, every time Kilauea erupts and lava pours into the sea.) Why do geysers occur at Yellowstone? (Groundwater is heated in hot rock near shallow magma bodies.) Apply Ask students to predict what will happen after the Pacific plate moves Hawaii away from the hot spot. (Volcanism will stop on Hawaii; a new island will form away from Hawaii.) learning modality: logical/ Converging Boundaries Many volcanoes form near converging plate boundaries where oceanic plates return to the mantle. Volcanoes may form where two oceanic plates collide or where an oceanic plate collides with a continental plate. Figure 19 shows how converging plates produce volcanoes. Many volcanoes occur near boundaries where two oceanic plates collide. Through subduction, the older, denser plate sinks beneath a deep-ocean trench into the mantle. Some of the rock above the subducting plate melts and forms magma. Because the magma is less dense than the surrounding rock, it rises toward the surface. Eventually, the magma breaks through the ocean floor, creating volcanoes. The resulting volcanoes create a string of islands called an island arc. The curve of an island arc echoes the curve of its deep-ocean trench. Major island arcs include Japan, New Zealand, Indonesia, the Philippines, the Aleutians, and the Caribbean islands. Volcanoes also occur where an oceanic plate is subducted beneath a continental plate. Collisions of this type produced the volcanoes of the Andes Mountains in South America and the volcanoes of the Pacific Northwest in the United States. Volcano Volcano Oceanic crust Continental crust Magma rising Subducting plate Key Asthenosphere Plate movement Subducting plate Subduction 206 ◆ mathematical L1 Skills Focus making models Materials plastic box, cold water, hot water, red food coloring, small narrownecked bottle, flat piece of plastic foam Time 15–20 minutes Tips Tell students to make sure that the water in the box is deeper than the height of the bottle. 206 Expected Outcome The “magma” rises out of the bottle and to the water’s surface, where it hits the “tectonic plate” in a spot directly above the bottle. When the plate is moved in one direction, the magma hits it in a spot behind the original spot. If the plate continued to move in the same direction, magma would hit it in a series of spots, with the newer volcanoes closer to the “hot spot” and the older volcanoes farther away from it. Extend Suggest that students continue the plate movement and number the volcanoes to show the sequence in which the volcanoes form. learning modality: kinesthetic sx05_TE_(nc6-6B).fm Page 207 Monday, June 6, 2005 11:10 AM Pacific Ocean Kauai Monitor Progress Maui Oahu Hawaiian I sla Hot Spot in a Box nd s Hawaii Motio n of Pacific plate Hot spot FIGURE 20 Hot Spot Volcanoes Eventually, the Pacific plate’s movement will carry the island of Hawaii away from the hot spot. Inferring Which island on the map formed first? Hot Spot Volcanoes Some volcanoes result from “hot spots” in Earth’s mantle. A hot spot is an area where material from deep within the mantle rises and then melts, forming magma. A volcano forms above a hot spot when magma erupts through the crust and reaches the surface. Some hot spot volcanoes lie in the middle of plates far from any plate boundaries. Other hot spots occur on or near plate boundaries. A hot spot in the ocean floor can gradually form a series of volcanic mountains. For example, the Hawaiian Islands formed one by one over millions of years as the Pacific plate drifted over a hot spot. Hot spots can also form under the continents. Yellowstone National Park in Wyoming marks a hot spot under the North American plate. 1. Fill a plastic box half full of cold water. This represents the mantle. 2. Mix red food coloring with hot water in a small, narrow-necked bottle to represent magma. 3. Hold your finger over the mouth of the bottle as you place the bottle in the center of the box. The mouth of the bottle must be under water. 4. Float a flat piece of plastic foam on the water above the bottle to model a tectonic plate. 5. Take your finger off the bottle and observe what happens to the “magma.” Making Models Move the plastic foam slowly along. Where does the magma touch the “plate”? How does this model a hot spot volcano? Answers Figure 4 Kauai An oceanic plate was subducted beneath a continental plate. Assess Reviewing Key Concepts L2 1. a. A weak spot in the crust where molten material reaches Earth’s surface b. at converging and diverging plate boundaries c. The crust is fractured, allowing magma to reach the surface. 2. a. An area where material rises from deep within the mantle and melts to form magma b. Through time, lava flows to the surface and forms new rock. The layers of rock accumulate to form a volcano. c. A series of volcanic mountains forms. Reteach L1 Have each student group make a chart showing the differences in how volcanoes form at diverging boundaries, converging boundaries, and hot spots. Performance Assessment L2 Have each student explain, in his or her own words, why volcanoes commonly occur along the boundaries of converging plates. 4 Teaching Resources Target Reading Skill Asking Questions Work with a partner to check the answers in your graphic organizer. • Section Summary: Volcanoes and Plate Reviewing Key Concepts 1. a. Defining What is a volcano? b. Reviewing Where are most volcanoes located? c. Relating Cause and Effect What causes volcanoes to form at a diverging plate boundary? 2. a. Defining What is a hot spot? b. Summarizing How does a hot spot volcano form? c. Predicting What features form as an oceanic plate moves across a hot spot? Travel Brochure As a travel agent, you are planning a Pacific Ocean cruise that will visit volcanoes in the Ring of Fire and Hawaii. Write a travel brochure describing the types of volcanoes the group will see and explaining why the volcanoes formed where they did. Chapter 6 Keep Students on Track See that students have selected the region that they will study. Possible topics for their research include myths and legends, the importance of volcanic soils, mineral resources, tourism, and geothermal power. Ask students to begin their research and start taking notes. To avoid duplication, check the regions and topics that student groups select. L2 Tectonics • Review and Reinforce: Volcanoes and Plate Tectonics • Enrich: Volcanoes and Plate Tectonics ◆ 207 Writing Skill Explanation Scoring Rubric 4 includes complete description of the types of volcanoes and how they form, and is written in a friendly, engaging tone 3 includes all criteria 2 includes description of one volcanic belt; other description is incomplete 1 includes incomplete or inaccurate descriptions of volcanic belts 207 sx05_TE_(nc6-6B).fm Page 208 Monday, June 6, 2005 11:10 AM Mapping Earthquakes L3 and Volcanoes Prepare for Inquiry Key Concept Earthquakes and volcanoes are concentrated together in belts. Skills Objectives Students will be able to • interpret data to plot the locations of earthquakes and volcanoes on a world map • observe areas in which earthquakes and volcanoes are concentrated • infer that earthquakes and volcanoes occur together in certain areas. Prep Time 20 minutes Class Time 40 minutes Teaching Resources • Skills Lab: Mapping Earthquakes and Volcanoes Advance Planning Photocopy an outline world map for each student. Guide Inquiry Invitation Remind students of the locations of recent earthquakes and volcanic eruptions. Introduce the Procedure Review the terms longitude and latitude and how to use those lines on the map to determine precise locations. Make sure that students know how to determine longitudes and latitudes that fall between lines. Troubleshooting the Experiment When students have plotted all locations, display a copy of the map that you have marked so students can check their work. Expected Outcome The marked map should indicate belts in which both volcanoes and earthquakes occur. 208 Mapping Earthquakes and Volcanoes Problem Is there a pattern in the locations of earthquakes and volcanoes? Skills Focus interpreting data Earthquakes and Volcanoes Earthquakes Volcanoes Longitude Latitude Longitude Latitude 120 º W 40 º N 150 º W 60 º N 110 º E 5º S 70 º W 35 º S Materials 77 º W 4º S 120 º W 45 º N • outline world map showing longitude and latitude • 4 pencils of different colors 88 º E 23 º N 61 º W 15 º N 121 º E 14 º S 105 º W 20 º N 34 º E 7º N 75 º W 0º 74 º W 44 º N 122 º W 40 º N 70 º W 30 º S 30 º E 40 º N 10 º E 45 º N 60 º E 30 º N 85 º W 13 º N 160 º E 55 º N 125 º E 23 º N 37 º E 3º S 30 º E 35 º N 145 º E 40 º N 140 º E 35 º N 120 º E 10 º S 12 º E 46 º N 14 º E 41 º N 75 º E 28 º N 105 º E 5º S 150 º W 61 º N 35 º E 15 º N 68 º W 47 º S 70 º W 30 º S Procedure 1. Use the information in the table to mark the location of each earthquake on the world map. Use a colored pencil to draw a letter E inside a circle at each earthquake location. 2. Use a pencil of a second color to mark the volcanoes on the world map. Indicate each volcano with the letter V inside a circle. 3. Use a third pencil to lightly shade the areas in which earthquakes are found. 4. Use a fourth colored pencil to lightly shade the areas in which volcanoes are found. Analyze and Conclude 1. Interpreting Data How are earthquakes distributed on the map? Are they scattered evenly or concentrated in zones? 2. Interpreting Data How are volcanoes distributed? Are they scattered evenly or concentrated in zones? 3. Inferring From your data, what can you infer about the relationship between earthquakes and volcanoes? 4. Communicating Suppose you added the locations of additional earthquakes and volcanoes to your map. Would the overall pattern of earthquakes and volcanoes change? Explain in writing why you think the pattern would or would not change. 175 º E 41 º S 175 º E 39 º S 121 º E 17 º N 123 º E 38 º N More to Explore On a map of the United States, locate active volcanoes and areas of earthquake activity. Determine the distance from your home to the nearest active volcano. 208 ◆ Analyze and Conclude 1., 2. Both earthquakes and volcanoes are concentrated in definite zones. 3. Earthquakes and volcanoes often occur in the same areas. 4. The pattern would not change very much. Additional data would be added to already apparent zones. Extend Inquiry More to Explore Provide copies of a U.S. map that includes insets for Alaska and Hawaii, and have students research and plot active volcanoes and recent earthquakes in the United States.